I'm not surprised that your individual quote is lower, given that interest rates are so low now, even (especially!) on long-term bonds.
1) They are getting a group rate. There is much less chance that the group, as a whole, will be a statistical outlier than you will be--law of averages. (and, bundled purchase along with other insurance for the company)
2) The company needs to roughly make people whole, based on what they have promised. so they may be paying their insurance company something to increase the return to make it work. They are paying to get out of their liability